This invention relates generally to a storage tank for half-raw semi-raw food material, that is, the food material that has undergone only preliminary processing treatment and needs to be processed further into an ultimate food or drink at some later time. It relates more particularly to a storage tank provided with a new and novel dispersion device.
In processing farming products into food and drinks, the seasonal nature of their supply prevents them from being processed at one time into the form of an ultimate or final food and/or drinks. Hence these products are usually stored in a partially processed state and occasionally are taken out from their storing place in required amounts for processing further into a food or a drink. For instance, when preparing a tomato ketchup or sauce starting from fresh tomatoes, the tomatoes are preliminarily or partially processed and stored in the form of a semi-raw material, such as a puree or pastes. The material thus stored in a semi-raw state can then be taken from their storing place in required amounts for final processing into a tomato ketchup or sauce. For such a series of processing steps, it is absolutely necessary that such semi-raw material should be stored under a completely germ-free condition. Today, a large-size tank is preferentially used for storage of such semi-raw material.
However, such a tank should be completely immune or free from any pollution such as that emanating from the tank itself and various tank accessories or from intrusion from outside of microorganisms during storage of the partially-processed material. The various methods and apparatus for germ-free storage of the half-raw food material proposed in the past are such as those disclosed in the U.S. Pat. Nos. 3,871,824; 3,918,678; 3,918,942; 3,951,184 and 3,998,589. These prior art methods and apparatus do not relate to the specific shape or structure of the storage tank contemplated from the viewpoint of effectively combatting against bacterialogical pollution of the stored material.
In a storage tank proposed in the prior art, a manhole device is provided horizontally at the top of the tank to permit access to the inside of the tank. The lid plate of the manhole is provided with delivery and discharge openings for a detergent or disinfectant solutions or a disinfected inert gas, as well as a peephole device for monitoring the inside of the tank. Because of the necessity for connecting these accessory devices to the manhole lid plate, protuberant portions were unavoidably formed in the connecting portions. These proturberant portions would turn out to be a "sink" for the semi-raw material and detract from germ-free maintenance of the storage tank.
Moreover, when the semi-raw food material is stored within a tank with a capacity of from 100 to 200 m..sup.3 for a prolonged time, the food material would have a concentration gradient, that is, the concentration of the material would differ from one point within the tank to the other. Since the semi-raw material is taken out from the tank in required amounts, it is necessary that the material be contained homogeneously in the tank. In the prior art storage tanks, no effective means are provided for keeping the homogeneity of the stored material.